1. Field of the Invention
The present invention relates to an antenna apparatus capable of measuring and compensating deformation and displacement thereof, which requires a highly reflector surface accuracy, a highly directional accuracy, and a highly tracking accuracy in astronomical observation and communication fields.
2. Description of the Related Art
In a recent radio telescope field, there is a strong demand to use a high frequency wave such as a submillimeter wave instead of a millimeter wave, for example. In order to perform the radio telescope observation using a high frequency wave, it is necessary to increase the reflector surface accuracy and the directional accuracy of a beam. On the other hand, in order to increase the observation efficiency, the telescope uses a large diameter lens and it is hope that a person can perform the astronomical observation day or night regardless of weather. However, the use of a large diameter lens increases a deformation of the telescope by its own weight, and strong wind and solar radiation on a bright day increase a heat deformation and stress deformation of the telescope. It is thereby difficult to keep a high reflector surface accuracy of the reflecting mirror and a directional accuracy of the beam. In order to obtain the telescope which can realize those various demands, the high reflector surface accuracy, the directional accuracy, the large diameter of the lens, and the observation in day or night on all weather, it is necessary for the antennal apparatus to have a compensation system to measure and compensate the reflector surface accuracy and a directional error of the reflecting mirror of the telescope in real time.
FIG.7 is a diagram showing a configuration of a conventional antenna apparatus capable of measuring a reflector surface accuracy of a reflecting mirror antenna based on Radio holography method, generating a control signal, and compensating the reflector surface based on the control signal. This technique has been disclosed in a following Japanese document:
MEASUREMENTS OF REFLECTOR SURFACE ACCURACY FOR 45 m RADIO TELESCOPE BASED ON RADIO HOLOGRAPHY METHOD, M. Ishiguro, K. Morita, et al., vol.62, No.5, pages 69-74, 1988, MITSUBISHI DENKI GIHO, MITSUBISHI DENKI KABUSHIKI KAISHA.
In FIG. 7, reference number 19 designates a communication satellite, 20 denotes a beacon radio wave transmitted. form the communication satellite 19, and 1 indicates a primary reflecting mirror made up of a plurality of panel reflector surfaces to be measured in the reflector surface accuracy. Reference number 21 designates a primary focus horn for receiving a conversing radio wave reflected by the primary reflecting mirror 1, and 22 denotes a reference antenna in a standard of the reflector surface accuracy. Reference number 23 designates a two channel correlation receiver, to which a power is supplied from the primary focus horn 21 and the reference antenna 22, for performing a correlation process. Reference number 4 indicates a secondary reflecting mirror support section for supporting the receiver 23.
Reference number 24 designates an electric field radiation signal, transferred from the receiver 23, having amplitude and phase of the electric field on the reflector surface to be measured using the reference antenna reflector surface as a standard.
Reference number 25 indicates a telescope driving system, 26 designates a driving signal for the telescope, 27 denotes attitude data of the telescope, 28 indicates an electric field radiation signal, and 17 denotes a reflector surface error calculation section. Reference character 10a designates reflector surface compensation data. Reference number 13 denotes a reflector surface compensation driving section.
Next, a description will now be given of the operation of the conventional antenna apparatus.
The primary focus horn 21 and the reference antenna 22 receive the beacon radio wave 20 transmitted from the communication satellite 19. The two channel correlation receiver 23 performs the correlation of those received data, so that one-dimensional electric field radiation signal 28 of the primary reflector surface is obtained using the reference antenna 22 as the standard.
A space pattern of the electric field radiation signal 28 in two dimensions is obtained based on the attitude data 27 of the telescope and the electric field radiation signal 28 in its attitude by performing the same measurement in changing of the attitude (or position) of the telescope around the direction of the radio wave source. Because there is a relationship of Fourier transformation between the electric field radiation pattern and the electric field distribution of an opening surface, it is possible to calculate the electric field distribution of the opening surface of the reflector surface by performing Fourier transformation of the electric field radiation pattern. An error of the reflector surface to be measured is thereby calculated by multiplying the term of the phase in the electric field distribution of the opening surface with the wavelength. The reflector surface compensation driving section 13 compensates the reflector surface error.
FIG. 8 is a diagram showing a configuration of another conventional antenna apparatus capable of detecting an antenna directional error, which has been disclosed in a following Japanese patent document.
Japanese laid-open publication number H3-3402, for example.
In FIG. 8, reference number 1 designates a primary reflecting mirror. Reference character 2a designates an antenna mount section. Reference number 29 designates a AZ angle detector in the antenna, 30 denotes a EL angle detector in the antenna, and 31 indicates the same means of the EL angle detector 30 or the mount only having the same case of the EL angle detector 30.
Reference number 32 designates a pair of beam generators mounted on the upper section of the AZ angle detector 29 fixed on the antenna frame 5a, and 33 denotes a light position detector mounted on the mount 31, to which the beam generated by the beam generator 32 is irradiated. Reference number 34 designates a beam generator mounted on both the EL angle detector 30 and the mount 31, and 35 denotes a light position detector mounted on the AZ angle detector 29, to which the beam generated by the beam generator 34 is irradiated.
Those light position detectors 33 and 35 form two divided photo diodes mounted so as to detect a deviation of the beam in Y-axis direction.
Next, a description will now be given of the operation of the conventional antenna apparatus.
The deformation of the antenna frame 5a generates a twist around the axis and a parallel displacement. In the system shown in FIG. 8, a pair of the light position detectors 33 for AZ axis and a pair of the light position detectors 35 for EL axis are mounted. By calculating the output from both the detectors 33 and 35, the magnitude of the twist in each of AZ and EL axis is detected. Further, the detected magnitude of the twist in each axis is compensated by adding or subtracting it with the angle signal detected by the EL angle detector 30 and 31 and the AZ angle detector 29.
Because the conventional antenna apparatus has the configuration described above, there is a drawback in the prior art in which it must be necessary to introduce the different systems and measurement methods, as shown in FIG. 7 and FIG. 8, in order to measure the deformation of the mount section which causes the reflector surface error and the directional error. This requires much labor and also increases the cost of the antenna apparatus.
In addition, the conventional antenna apparatus shown in FIG. 7 involves another drawback which must require to perform the another radio wave holography observation using an artificial radio wave generator in order to measure the reflector surface error in addition to the astronomical observation. This conventional drawback decreases the operation efficiency for the antenna apparatus. Still further, the conventional antenna apparatus cannot operate in real time because it is difficult to compensate the deformation of the reflector surface caused by changing the amount of the sunlight and the wind and the attitude (or position) of the telescope at every moment during the astronomical observation.
Still furthermore, although the antenna angle detector in the conventional antenna apparatus shown in FIG. 8 can measure the directional error of the telescope beam when the twist of AZ axis and EL axis occurs by the deformation of the antenna frame, there is a problem that it is difficult to measure the directional error caused by the displacement of the primary reflecting mirror and the secondary reflecting mirror. In addition, in the system using the light position detector, there is a drawback that it is difficult to mount the light position detector in the place where no light beam reaches in the system using the light position detector. Therefore this drawback limits the place where the antenna is introduced and mounted.